In activity involving paints and varnishes, widespread use is made of diisocyanates, especially alkylene diisocyanates (Tolonate) and their derivatives of biuret type or their trimers.
However, two problems remain unsolved at present, namely:
the use of organic solvent, the presence of which is believed to be toxic and detrimental to the environment; PA1 the need to market nonvolatile products, which has led to making the molecules heavier, this being done by oligomerizing the diisocyanates; this solution is not satisfactory because it employs an intricate, and hence expensive, functional group to solve the problem. PA1 where the R.sub.1, R.sub.2 and R.sub.3 which are similar or different, denote a hydrogen or a group chosen from: PA1 hydrocarbon chains of 1 to 12 carbon atoms, especially alkyls, including aralkyls, aryls, alkoxys and silyls; PA1 unreactive halogen atoms (fluorine, and even chlorine); PA1 electron-withdrawing functional groups advantageously comprising the carbonyl group, such as alkoxycarbonyl hydroxycarbonyl (carboxylic acid) or aminocarbonyl (amide); PA1 where the Ls, which are similar or different, denote a divalent (advantageously omega, omega prime) hydrocarbon radical of 2 to 12 carbon atoms, advantageously of formula: EQU --Y--L'--Y'--(NH--CO).sub.z -- (Formula 2) PA1 either a single bond; PA1 or a group chosen from the following groups: PA1 --R.sub.5)C(R.sub.6)--, --NR.sub.4 --, O or --S--; with R.sub.5, R.sub.6 and R.sub.4 denoting a hydrogen or a group chosen from: PA1 hydrocarbon radicals of 1 to 12 (advantageously of 1 to 4) carbon atoms, especially alkyls, aryls, aralkyls and silyls; PA1 unreactive halogen atoms (fluorine, or even chlorine); PA1 where A denotes an organic backbone which has n free valencies, n being between 2 and 7 (closed intervals advantageously between 2 (not including this value) and 4, and n being equal to p+q; PA1 where NCOblock denotes a protected isocyanate functional group; PA1 where p is between 1 and 6, advantageously between 1 and 3, preferably between 1.5 and 2.5 (closed intervals); PA1 where q is between 1 and 6 (closed interval), advantageously greater than 1 and not exceeding 3 (semiopen, semiclosed interval), preferably not exceeding 2 (semiopen, semiclosed interval). PA1 ethylenic monomers of isoprene, 1,3-butadiene, vinylidene chloride or acrylonitrile type, PA1 vinylaromatic monomers such as styrene, bromostyrans, alpha-methylstyrene, ethylstyrene, vinyltoluene, chlorostyrene or vinylnaphthalene, PA1 alkenoic acids, esters or anhydrides such as acrylic and methacrylic acids, alkyl acrylates and methacrylates in which the alkyl group has 3 to 10 carbon atoms, hydoxyalkyl acrylates and esters of ethylenic acids containing 4 or 5 carbon atoms. PA1 the introduction, during the polymerization of the monomer(s) forming the latex particles, of a monomer according to the invention in suspension in a proportion of the, or of one of the, monomers, and PA1 overpolymerization (in the sense of an epipolymerization), which consists of a synthesis of the type sometimes referred to as "core-shell": a latex seed is overpolymerized with the (co)monomer(s) in the presence of initiator and of a surfactant. The monomer according to the invention, in suspension in a proportion of (co)monomer(s), is introduced at the end of polymerization so as to obtain latex beads of a precise and narrow particle size distribution, in which the monomer according to the invention is grafted at a more or less great distance from the particle core.